Presently, there is a need for cutting casts and other rigid objects (e.g. helmets, dry wall, bone or frozen material, etc.). For example, casts are rigid dressings which are used to immobilize broken bones and the like. Casts may be made from materials such as plaster or layered fiberglass set with resin. Generally, removal of such rigid casts requires use of some cutting device.
Any cutting requires relative motion between the material being cut and a blade. Normally this is achieved by rotating the blade or moving the blade in long linear strokes. For example, industrial cutting devices of the past have most often used rotating or reciprocating blades to cut through rigid materials such as plaster or fiberglass/resin material, but such cutting modes are generally considered too dangerous for use in removing casts from patients due to the close proximity of the cast to the patient. Such cutting blades can also be dangerous to the user. Therefore, a preferred action is one which provides relatively short oscillating strokes of a blade. Instead of rotating or reciprocating blades, medical cutting devices typically use oscillating serrated or toothed blades which are considered safer.
In theory, oscillating blades with a relatively small angle of oscillation (e.g. less than 15.degree.) show relatively little tendency to cut skin or soft tissues (i.e. soft low mass materials) since these materials tend to move or jiggle along with the blade movement rather than be cut (i.e. eliminating the relative motion required for cutting). More rigid materials with greater mass tend to remain stationary and, thus, allow the relative motion required for cutting. Rigid materials with appreciable mass, including plaster and multi-layer fiberglass casts, are readily cut using an oscillating blade operating at motor speeds of 12,000-20,000 rpm. The best cutting performance is typically obtained at higher speeds, particularly speeds which are above the resonant frequencies of typical cast materials.
The relative motion between the materials being cut and the serrated or toothed blade is reduced by the friction between the two causing the material being cut to move with the blade and the cutting device driving the blade to oscillate opposite the blade ("friction movement") thereby reducing the blade's relative movement and efficiency. This friction movement is preferably minimized because it reduces the efficiency of the cutting device and adds to the fatigue of the user. Cutting devices of the past suffer from significant inefficiency due to friction movement.
Cutting devices generally include a motor, a handle, and a cutting blade. Devices of the past are both bulky and poorly designed from ergonomic and efficiency perspectives. Generally, the motors used in such devices are heavy, noisy, and may produce excessive heat. Many devices use line-voltage A/C brush-type motors that require fans and open air vents to provide sufficient airflow to cool the motor during use. This configuration is inherently noisy, relatively inefficient, and cutting residue and dust may be drawn into the motor and other components by the necessary flow of cooling air.
In addition, such devices have typically been designed with the motor positioned in-line with the handle and cutting blade positioned linearly along the handle whereby the handle is between the cutting blade and the motor (i.e. the weight of the motor is generally behind the hand position on the handle (opposite the cutting blade) when the device is used to cut). This design provides a device which is not balanced and has a low moment of inertia with which to resist the device's tendency to oscillate opposite the blade. Therefore, devices with this design are difficult to use and are inefficient at cutting. Still other devices are designed with the motor positioned encased within the handle. This design provides a device which is bulky to hold and, therefore, is difficult to use. In addition, these devices tend to be under powered, are not balanced and have a low moment of inertia with which to resist the device's tendency to oscillate opposite the blade. Furthermore, the heat generated by the device is usually conducted to the handle which is uncomfortable to the user and even to the patient.
The general method of use of such cutting devices is to plunge-feed the cutting blade into, through, and out of the cast (or other rigid material) at a first static location and then repeat the in, through, and out procedure at second, third, . . . etc. locations. Each cut results in a single elongated slot puncture in the cast. The cast is easily removed once a lengthwise cut is formed by stringing together a plurality of such single cuts. The design of prior cutting devices, explained above, wherein the motor and cutting blade are on opposite ends of a handle, results in one end of the cutting device being much heavier than the other end. This lack of balance makes the device difficult to control and use, since the cantilevered weight of the motor must be supported and resisted by the user's wrist muscles.
To provide an oscillating blade, most cast cutting saws of the past have used a "Y" shaped yoke, an eccentric cam attached to a shaft of the motor (which typically extends through the handle) and positioned between tines at the forked end of the yoke, and the cutting blade attached to a stem at the opposite end of the yoke. As the motor rotates the eccentric cam, the forked end of the yoke moves from side-to-side which, in turn, moves the stem end of the yoke thereby oscillating the cutting blade (usually between 5.degree.-20.degree.). Thus, rotational movement of the eccentric cam is translated into oscillating movement of the cutting blade.
For these types of cutting devices the eccentric cam must be sized to precisely fit between the tines. If there is space between the cam and the tines, the device will be noisy when in use. The loudness of the device is important because it both frightens patients and hinders communication. However, if the eccentric cam precisely fits the space between the tines, thereby minimizing noise production, the friction between the eccentric cam and the tines will produce heat. Heat production is a problem because, depending on the materials involved, the heat could be conducted back to the motor, through the handle, or down to the cutting blade. If heat is conducted to the motor, it could have adverse effects including shortening the life of the motor. If heat is conducted through the handle or to the cutting blade, it could result in burning the user or the patient if they come into contact with either the handle or the cutting blade.
A further problem of these prior devices is they lack braking mechanisms and merely allow the blades of these devices to rotate or oscillate several hundred cycles before coming to a full and complete stop. This can take up to several seconds. A better braking mechanism is needed.
An additional problem is the removal of cutting residue and dust which is created when the cast or other rigid object is cut. Some cutting devices of the past have included vacuum systems to help collect such residue and dust. However, these vacuum systems have not been integral parts of the cutting device. Rather, they have tended to be clumsy attachments which are awkward and inefficient. In addition, these vacuum systems do not typically provide unobstructed vacuum passageways and, therefore, suffer inefficiencies in removing cutting residue or dust.
In general, prior cutting devices suffer from excess noise, heat build-up, inefficiencies, poor design and weight distribution, and/or operate at speeds and power levels that are less than optimal for the materials they are expected to cut.